This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The incomplete digestion of proteins by proteases is a hindrance in their characterization by mass spectrometry. Some proteins are hard to digest due to aggregation. In order to increase the digestion efficiency of proteases we have developed an on-line high pressure digestion system. This system uses UPLC technology to increase the digestion pressure to a maximum of 10,000 psi.